1. Field of the Invention
The present invention generally relates to lightwave communications systems and, more particularly, to a method and apparatus for transmitting optical pulses having variable pulse widths.
2. Description of the Related Art
In the field of fiber optic communications, it has been known for some time to increase the capacity of an optical communications link by propagating wavelength-division multiplexed (WDM) optical signals along optical fibers. Specifically, a WDM signal is composed of a plurality of distinct wavelengths of light, each such wavelength carrying a respective optical information signal, also known as an information channel. The number of wavelengths (i.e., information channels) in a WDM signal is a system parameter and usually ranges from 2 to over 100 (in the case of “dense” WDM, or DWDM).
Chromatic dispersion can be a limiting factor in such optical transmission systems. Chromatic dispersion is the tendency of a pulse of light propagating through an optical fiber to broaden due to the phenomenon that different wavelengths of light pass through the fiber at different speeds. While such dispersion is useful for suppressing non-linear effects, such as four-wave mixing and self-phase modulation, too much dispersion easily causes intersymbol interference. Normally, dispersion in the transmission fiber is reduced by periodic use of a dispersion compensation device in the various network elements of the optical transmission system. However, a single dispersion compensation device in each network element typically cannot provide the same average dispersion for all optical signals of a WDM transmission system (i.e., the extent of average dispersion for optical signals having different wavelengths varies). This may force a designer of optical transmission systems to employ multiple dispersion compensation devices, both inline, and at the end terminal. The use of multiple dispersion compensation devices results in increased system complexity and additional cost.